Movement of Materials Through the Cell Membrane

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Movement of Materials Through the Cell Membrane

• all cells are found in a liquid environment
  because it makes it easier for materials such as
  food, oxygen, and water to move in and out of a
  cell.

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Cell Membrane
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Importance

• Maintains chemical balance within the cell
• (HOMEOSTASIS)

How?

1. Selectively permeable-allows passage of some
   materials in/out, but keeps others out.

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Passive Transport

• no energy is required to move materials.
• Diffusion
• Osmosis
• Facilitated Diffusion

Follows a concentration gradient-difference in
concentration of molecules
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Diffusion

• process by which molecules of a substance move
  from areas of higher concentrations to areas of
  lower concentrations.
• (air freshener, small molecules in/out cells,
  etc.)

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Diffusion
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2 factors determining diffusion continued

• Permeability
• If a substance can diffuse across a membrane, the
  membrane is considered permeable. If a substance
  cannot diffuse across a membrane, the membrane is
  considered impermeable.

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Diffusion
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2 factors determining diffusion

• Concentration Level
• if 2 substances are present in unequal amounts on
  either side of a membrane, each substance will
  try and move to an area of less concentration
  until equilibrium is reached.

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Diffusion
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Osmosis

• diffusion of water across a selectively permeable
  membrane from a higher concentration to a lower
  concentration.
• force exerted by osmosis is called osmotic
  pressure (plants it is called turgor)
• can cause serious problems for cells because
  water may rush into a cell causing it to burst
  because there is a lot of material in a cell

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Osmosis Example
Osmotic pressure if walls dont give
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Osmosis In Action
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Plant Cells (observing osmosis)
Turgor pressure
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Cells In Different Solutions
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How do cells deal?

• many organisms do not come in contact with fresh
  water, so cells are bathed in different liquids
  (such as blood) that have concentrations of
  dissolved materials roughly equal to cells
  themselves
• plants and some bacteria have a cell wall that
  does not allow for expansion (but now vulnerable
  to injuries to cell wall)
• other cells pump out the water that is forced in
  by a contracting a vacuole
  

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Facilitated Diffusion

• Passive transport of materials across the plasma
  membrane by means of transport proteins
• Convenient openings for molecules to pass through
• (amino acids, sugars)

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Facilitated Diffusion (diagram)
High Concentration
Low Concentration
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Active Transport

• (energy is required) where a carrier protein
  moves material across the concentration gradient
  (from low to high).
• Molecular pumps bring in calcium (Ca), potassium
  (K), and sodium Na) ions
• Endocytosis, exocytosis

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Endocytosis

• endocytosis-taking in large amounts of materials
  by the in-folding (pockets) of cell membrane,
  where pocket breaks loose from the outer portion
  of the cell membrane and forms a vacuole within
  the cytoplasm
• phagocytosis-large particles/small organisms are
  taken into the cell by endocytosis
• pinocytosis-tiny pockets fill with liquid and
  pinch off to form vacuoles within the cell

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Phagocytosis/Pinocytosis
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Exocytosis

• contents of cell are forced out when materials
  surround it and push it out
• (Wastes, specific molecules harmful to inner
  cell)

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Endocytosis Exocytosis at Work
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Active Transport (diagram)